Balloon angioplasty is a medical procedure to widen obstructed blood vessels narrowed by plaque deposits. The procedure may be used in coronary or peripheral arteries. In an angioplasty procedure, a catheter having a special inflatable balloon on its distal end is navigated through the patient's arteries and is advanced through the artery to be treated to position the balloon within the narrowed region (stenosis). The region of the stenosis is expanded by inflating the balloon under pressure to forcibly widen the artery. After the artery has been widened, the balloon is deflated and the catheter is removed from the patient.
A significant difficulty associated with balloon angioplasty is that in a considerable number of cases the artery may again become obstructed in the same region where the balloon angioplasty had been performed. The repeat obstruction may be immediate (abrupt reclosure), which is usually caused by an intimal flap or a segment of plaque or plaque-laden tissue that loosens or breaks free as a result of the damage done to the arterial wall during the balloon angioplasty. Such abrupt reclosure may block the artery requiring emergency surgery which, if not performed immediately, may result in a myocardial infarction and, possibly, death. This risk also necessitates the presence of a surgical team ready to perform such emergency surgery when performing balloon angioplasty procedures. More commonly, a restenosis may occur at a later time, for example, two or more months after the angioplasty for reasons not fully understood and which may require repeat balloon angioplasty or bypass surgery. When such longer term restenosis occurs, it usually is more similar to the original stenosis, that is, it is in the form of cell proliferation and renewed plaque deposition in and on the arterial wall.
To reduce the incidence of re-obstruction and restenosis, several strategies have been developed. Implantable devices, such as stents, have been used to reduce the rate of angioplasty related re-obstruction and restenosis by about half. The use of such intraluminal devices has greatly improved the prognosis of these patients. The stent is placed inside the blood vessel after the angioplasty has been performed. A catheter typically is used to deliver the stent to the arterial site to be treated. The stent may further include one or more therapeutic substance(s) impregnated or coated thereon to limit re-obstruction and/or restenosis.
Numerous stent designs are known in the art. One type of stent design includes a cylindrical body formed from metallic struts. The struts form a lattice-like surface that may be rolled into a small diameter cylinder (i.e., a compressed form). The stent is positioned (e.g., compressed) onto a balloon of a catheter for subsequent deployment. It is often desirable to provide a small profile size of the stent while it is positioned onto the balloon. When positioned within the blood vessel, the balloon and stent may be expanded together. After deployment, the balloon is deflated and the metal stent is left plastically deformed and left within the vessel in an expanded form. Metallic stents are generally strong and able to withstand the shear forces present in the vasculature. Metallic stents, however, are generally not biodegradable. Therefore, metallic stents may remain within the vasculature and may have to be retrieved under certain circumstances.
Another type of stent design includes a cylindrical body formed from a tubular braided mesh of fabric (non-metallic) material. The braided mesh may be biodegradable (i.e., degrades in a controlled manner within the patient). Once the fabric stent is positioned properly, it self-expands into a larger diameter. Mesh stents can be made to be biodegradable. However, they sometimes lack sufficient mechanical strength to withstand the shear forces present in the vasculature.
Accordingly, it would be desirable to provide a hybrid biodegradable/non-biodegradable stent, delivery system, and method of treating a vascular condition that would overcome the aforementioned and other limitations.